I'm assuming that this program is an application of some sort and not a device driver. Because it is starting automatically, it probably has a shortcut in the Startup folder, either for an individual user or for the All Users profile.
The simplest way to find out is to right-click the Start button and select Explore All Users from the flyout menu. Expand the tree to Start Menu | Programs | Startup. There should be a shortcut to the application in the left pane of the window. Delete the shortcut and that keeps it from starting.